Clothes washing machines commonly extract water from the clothes (fabrics) by revolving a perforated container or basket containing the fabrics at a high rotational velocity. Centrifugal forces pull the majority of the water out of the cloth fibers and through the holes in the rotating basket. The water is removed from the machine by means of a pump and/or drain arrangement. The rotating basket is supported by a suspension system designed to dampen translational motion induced by any imbalance within the rotating basket. High stresses are encountered within the basket, drive system, and suspension system during the high speed spin action used for water extraction during normal wash cycles. With an imbalance within the load, the normal force is generated which is proportional to the product of the mass, the distance between the imbalance and the center of rotation, and the square of the velocity. Small imbalances can very easily generate large forces as a result of the high rotational velocities. In accordance with one aspect of the present invention, the size of the imbalance, and thereby the forces acting upon the rotational system, are minimized.
It is well known for a washing machine to employ a sensor to determine if the machine is operating with an unbalanced load. If an unbalanced load is detected during an extraction spin cycle, the machine is stopped and a signal is generated to alert the user to the unbalanced load. Another common method of dealing with an unbalanced load is to design the drive system of the washer so that an unbalanced load will require greater torque to reach terminal spin velocity than what is available. Since the torque output of the motor is fixed, the load never reaches terminal spin velocity. The spin velocity is thus adjusted, via a slip mechanism in the drive system, to a lower value.
The sensor approach has the advantage of being able to alert the consumer to an unbalanced condition. If the consumer rebalances each load that is detected as being unbalanced, every load will spin at full speed. However, the disadvantages to the sensor scheme far outnumber the benefits. If the user is not aware of the unbalanced condition, the load in the basket will remain saturated. Imbalance sensors have also been shown to produce unnecessary service (repair) calls. A user finding the machine stopped with a load of saturated clothes, may call for service when all that is needed is for the fabrics to be redistributed and the machine restarted. A further drawback of an imbalance sensor is the cost of the sensor itself. With increasing material consciousness, the addition of a sensor for a function that can be implemented without a sensor is difficult to justify. In accordance with another aspect of the present invention an imbalance present in the wash load of fabrics is detected and the terminal spin speed is adjusted to an appropriate level without the need for an imbalance sensor or a slip mechanism in the washing machine.
Spin control is accomplished using a set of algorithms. An additional algorithm is employed for controlled braking of the rotating clothes basket. It is advantageous that the rotating mechanisms of a washing machine be stopped quickly when the lid is opened. For example, Underwriter's Laboratory requires, that the rotating mechanisms within a washing machine reach a full stop within seven seconds of opening the lid. Current production washers typically meet this requirement with a friction type brake contained within the transmission housing. When the lid is raised, the power supply to the motor is interrupted and the brake engaged. The result is an abrupt halt in the rotational action. The mechanical brake has proven itself effective; however, new washer designs have eliminated the transmission and, indirectly, the mechanical brake. Since these designs must conform to the same stopping requirements as prior mechanically braked washers, the brake function must be implemented other than by us of the transmission. The motor may be constructed to contain a mechanical brake or an external brake could be placed around the motor drive shaft. Each of these approaches adds cost and complexity to the machine. In accordance with one aspect of the present invention rotating components are braked by electronically controlling the motor, without the addition of mechanical hardware.
A direct drive oscillating basket washing machine and associated of the type of the exemplification machine and control are disclosed in U.S. Pat. No. 5,076,076, issued to Thomas R. Payne on Dec. 31, 1991, and assigned to General Electric Company, assignee of the present invention; which patent is included herein by reference.